Historically, tracing a call through a telephone switching system to identify the calling station has typically included the assistance of telephone company personnel. Thus, a party receiving, for example, a nuisance call would have telephone company personnel notified to trace the identity of the calling station while the nuisance call continued. With older telecommunication systems, this requirred telephone company personnel to first translate the called station's directory number to an equipment location and then physically trace the call connection through the switching system to the calling station equipment location. When associated with a calling station connected directly to the same switching system, the equipment location can easily be translated to a local calling station directory number. Alternatively, when the equipment location is associated with a trunk to a distant switching system, personnel in the distant switching system office would have to trace the call to the calling station or to still another office until the calling station is identified. As a result, the call tracing process may take a considerable period of time. Of course, the nuisance caller is not going to continue the call for any extended period of time particularly if the caller is trying to avoid detection.
Stored program-controlled switching systems eliminate the need of physically tracing a call through an office; however, the problem of notifying telephone company personnel to trace a nuisance call is still required. Typically, the switching system program may be modified to identify all calls to a particular called station. Similarly, specialized equipment at the telephone office may be utilized to identify nuisance callers; however, again, the need for arranging for this type of tracing equipment in advance of the nuisance call is required. Nevertheless, call tracing may still be thwarted when an interoffice nuisance call is made.
Display station sets offer some relief to the problem of having to arrange for call tracing in advance. Here, the station set which is usually associated with a private branch exchange displays the intraexchange calling station identity when the called station set is rung. However, the problem of identifying a nuisance caller is likewise thwarted with an interoffice call. Furthermore, the problem of generating a permanent record for the authorities also arises unless prior arrangements with telephone company personnel have been made in advance. Even with a record of all calls to a particular called station, the problem of distinguishing which calls are nuisance presents itself unless the nuisance caller uses the same calling station.